Living Longer, the Lemur Way is a Lesson in Life
In a recent article published in the journal Behavioral Ecology, researchers believe that they may have found one reason why female lemurs of a species known as Propithecus edwardsi―a rainforest-dweller with orange-red eyes, a black face and woolly dark brown fur―live longer than their male counterparts: sticking to a social group in old age.
What makes the Propithecus edwardsi lemur significant is that unlike the majority of animal species where males and females differ significantly in their physical phenotype and risk-promoting hormone levels that often lessen the survivability of flamboyant and aggressive males over more subdued females, both sexes actually are almost physically indistinguishable and have similar levels of testosterone.
Researchers living in the wild in Ranomafana National Park in southeastern Madagascar with the Propithecus edwardsi lemur have observed that one difference between the males and females studied is that the males tend to die by their late teens whereas the females survive into their 30s. This discovery was the result of 23 years of observation and study from the mid-eighties to 2009.
One aspect of social life that both sexes share is the switching of social groups known as “dispersal behavior” where individual lemurs will leave their social group in search of a new one for as-of-yet undetermined reasons. This behavior, however, puts a lemur at risk of starvation, increased exposure to predators and potential bodily injury from other lemurs as a lemur attempts to establish itself as the new kid on the block.
"When you're a social animal and you go off on your own into unfamiliar territory, finding food can be more of a challenge. Plus you don't have the extra protection of other group members who can help look out for predators. Even when you find a new group to join, you may have to fight your way in and there's a chance of getting injured in a fight," said co-author Jennifer Verdolin of the National Evolutionary Synthesis Center in Durham, North Carolina.
Although both male and female lemurs exhibit repeated dispersal behavior, the sexes differ in one significant way―while females tend to finally settle down to one social group by the time they reach age 11, the males continue to wander in search of new social groups throughout their lives. The result of being a rolling stone is believed to come at the cost of a shortened lifespan for males in comparison to females.
Although extrapolating these findings to humans is a bit of a stretch, the authors of the study point out that analyzing risk-taking behavior at different ages could reveal age-specific mortality risk factors that researchers previously have not considered in studying longevity differences between males and females.
Image Source: Courtesy of Wikipedia
Reference: "Risky business: Sex differences in mortality and dispersal in a polygynous, monomorphic lemur." Behavioral Ecology (First published online: February 28, 2013); Tecot, S., B. Gerber, et al.